1. Field of the Invention
This invention relates to a process for the conversion of a gaseous paraffinic feed containing ethane to liquid aromatics in the presence of a crystalline zeolite catalyst.
2. Description of the Prior Art
Zeolites and alumina have been used in the past in the preparation of catalysts for the production of aromatic hydrocarbons from open chain hydrocarbons. The open chain hydrocarbon is passed over the catalyst at an elevated temperature in the liquid or vapor phase. Zeolites of various types, particularly those containing a high silica-to-alumina ratio, have been suggested for the preparation of such catalysts. Examples of such zeolites are mordenite and the ZSM varieties. Such zeolites have been known to contain gallium in the form of its oxide which is substituted either partially or wholly for the aluminium oxide present therein. These zeolites however contain gallium as part of the crystal structure of the zeolite and the gallium is non-ionic. However, the yields of aromatic hydrocarbons from such open chain hydrocarbons have been unsatisfactory when using catalysts prepared from such zeolites.
U.S. Pat. No. 4,180,689 teaches that by using catalysts which contain gallium and which are prepared from specific types of aluminosilicates improved yields of aromatic hydrocarbons may be obtained if gallium-containing catalysts are prepared from specific types of aluminosilicates. This patent further discloses that if the gallium is either exchanged for one of the cations or protons or impregnated into the zeolite cavities surprisingly high catalytic activity is obtained especially in hydrocarbon conversion process. The feedstocks for this process are C.sub.3 -C.sub.12 feedstock of either a single component or mixtures of saturated and unsaturated hydrocarbons.
U.S. Pat. No. 4,120,910 discloses that aromatic compounds can be produced by contacting, in the absence of added air or oxygen under suitable conversion conditions a gaseous, paraffinic feed stock containing a high percentage of ethane with a ZSM-5 type crystalline aluminosilicate zeolite catalyst having incorporated therein a minor amount of a metal or metal oxide from Group VIII, IIB, or IB. Especially preferred is a zinc-copper mixture.